Indium tin oxide (ITO) ceramics are used for the manufacture of sputtering targets, which in turn are used to produce transparent conductive thin films for optoelectronic applications, such as thin film photovoltaic cells, flat panel displays, touch panels, architectural and automotive glazing, organic and inorganic LED applications. ITO ceramics with In2O3 contents of 98-80 wt. % are reliable materials for these applications and provide high quality thin films. However, as the demand for Indium and Indium-based materials has increased, In metal price has also increased. Consequently, ITO sputtering target cost has increased considerably over the last twenty years.
ITO ceramic targets used in vacuum sputtering deposition methods for the formation of high quality transparent conductive oxide (TCO) thin films must generally have high densities. Additionally, conventional ITO thin films, as well as ZnO-based thin films and some other transparent conductive oxide thin films, are not very stable in certain environments, e.g. in resistive touch panels and flexible photovoltaic applications, which may impact their useful lifetime.
ITO ceramics usually consist of In2O3 (or indium-sesqui-oxide) grains, where tin partially substitutes indium in the crystalline lattice of In2O3. When SnO2 content in ITO ceramics is 6 wt. % or greater, a secondary phase, In4Sn3O12, is also present. The content and grain size of this secondary phase may be defined not only by the In2O3/SnO2 ratio, but also by the manufacturing features such as starting materials, process uniformity, firing conditions, and size of the producing ceramic bodies, among others. The content and distribution of this secondary phase may also affect the sputtering stability of the target such as its sensitivity for arcing in a DC process, and, as a result, the film quality and reproducibility.